Intrinsic Mechanism Of Zebrafish Behavioral Response Under Combined Exposure Of Two Contaminants

Water environment pollution has seriously threatened the living environment of aquatic organisms and human beings.With the progress of industrialization and the progress of agricultural production,the problem of global water pollution is becoming more and more serious.Pesticides and heavy metals are the most important pollutants in water environment,while pollutants entering the water environment will seriously destroy the living environment of aquatic organisms and cause water ecosystem disorders.Aquatic organisms have their regulatory mechanism aim at the polluted water environment,in which the change of aquatic biological behavior is the change of the external environment and internal environment.The change of behavior can reflect whether organism can survive normally,so the behavior change model can be constructed according to the law of biological behavior toxicity response.In recent years,the study of aquatic biological behavior has gradually been paid attention to,which provides important theoretical basis and practical guidance for the prevention and control of environmental pollution.Acetylcholinesterase is a key enzyme in the process of nerve conduction,and the change of AChE activity can be used as a biomarker of water pollution.The external behavior and internal secretion of the aquatic organisms will be changed under external environmental stress and there may be some relationship between AChE and external behavior.This paper selects deltamethrin and cadmium chloride as pollutants,using zebra fish as test organisms.Determine zebra fish behavior response of joint toxicity under the exposure of 48h(0TU,0.1TU,1TU,2TU four concentration group)under the condition of pollutants in different concentrations and combinations(Based on a 48 hour median lethal dose of LC50-48 h,a toxicity unit of 1 TU was set up for this contaminant as zebra fish’s LC50-48h),simultaneous determination of zebra fish muscle AChE activity changes in different exposure time(0 h,0.5 h,1 h,2 h,4 h,8 h,16 h,32 h and 48 h).In order to explore the internal mechanism of behavior response under two kinds of pollutants combined,correlation analysis between muscle AChE and behavior strength of zebra fish behavior was made.The results show that:(1)Zebra fish acute toxicity of two pollutants exposure test results showed that LC50-48 h of deltamethrin on zebra fish was 5.2 ug/L,LC50-48 h of cadmium chloride on zebra fish was 42.6 mg/L.The results indicate that deltamethrin is a highly toxic compound in zebrafish,while cadmium chloride is a high toxic compound.(2)Zebra fish in deltamethrin exposure combined with cadmium chloride in(10:0,7:3,5:5,3:7,0:10),the AChE activity of zebra fish muscle tended to decrease with the exposure concentration and exposure time,and the inhibition ratio of two different pollutants on muscle AChE was not the same.The degree of AChE inhibition was increased with the increase of the concentration.In lower concentration exposure,the inhibition rate of AChE is low,sometimes even though AChE was inhibited relatively large but can be restored to a relatively high level which indicated that zebra fish has a better adjustment ability in the lower concentration than in high concentration.The AChE activity decreased rapidly in 0-0.5h with different proportions in the 1TU group then the enzyme inhibition curves in constant fluctuation,the fluctuation times is more than under 0.1TU treatment which shows that the toxic effect in 1 TU concentration is greater than in 0.1 TU.In 2 TU group,it was difficult to recover to a relatively high level after AChE was inhibited indicating that the under higher concentration exposure,the toxicity of zebrafish is more obvious and has irreversible effect.(3)In the analysis of 48 h behavioral toxicity,the average value of the behavior strength of zebra fish at lower concentrations(0.1TU)of the two kinds of pollutant exposure bigger than higher concentration(1 TU and 2 TU)exposure,zebra fish behavior is relatively smooth to adjust;in 1 TU and 2 TU exposure in zebra fish the behavior gradually adjust to the toxicity effect of death or to adjust the toxic effects after death or adjust or adapt to the process.(4)The changes of AChE and behavior strength of the every concentrations were consistent with the stepwise response model of environmental behavior under two kinds of pollutants exposure.The correlation analysis of zebra fish behavior strength and AChE inhibition showed the results that in the experimental group toxic effect from inhibit AChE to influence behavior had 2h delay under deltamethrin exposure.When deltamethrin: cadmium chloride was 7:3 ratio,the delay effects of 0.1TU is 0.5h,1TU and 2TU is 2h.When deltamethrin: cadmium chloride was 5:5 ratio,0.1TU group had 2h delay,1TU group did not had delay.There was no correlation between AChE and the behavior strength of each group under cadmium chloride and 3:7 ratio.The correlation analysis shown that under the effect of deltamethrin,inhibition of zebrafish muscle AChE is one of the factors which cause behavior change and toxic effect from inhibit AChE to influence behavior has 2h delay.Under the combined toxicity,the duration of the delay is complex,which can be related to the proportion of deltamethrin in the mixed pollutants.Cadmium chloride had no significant correlation between enzyme inhibition and behavioral toxicity.The results provide theoretical basis for the study of neural conduction and extrinsic behavior in zebrafish.